1. Field of the Invention
The present invention relates to a grinding machine for sharpening saw chain.
2. Description of the Prior Art
There are different types of saw chain with the different types being determined in general by the different shapes of the cutter teeth in such chain. The two most common types of saw chain have hook-shaped cutter teeth. One such common type, called the "chipper" or "round tooth" chain, has generally curved hook-shaped cutter teeth. The other common type, the so-called "chisel bit" chain, has generally L-shaped cutter teeth with the side and top portions of each tooth meeting at a sharp corner.
Grinding machines have been devised to sharpen both such types of saw chain using a disc-shaped grinding wheel. However, it has been found that for best chain performance the cutter teeth of these different types of chain should be sharpened at different angular positions along the peripheral edge of the grinding wheel. For example, with the chipper chain it is desirable to position the cutter tooth for sharpening at the center of the peripheral edge of the wheel as determined by a median plane passing through the center axis of the wheel perpendicular to the plane of the wheel. The center point of grinding is where the median plane intersects the peripheral edge of the wheel. However, with the chisel bit chain, the preferred angular position along the wheel is at about 45 degrees from the center point of grinding as measured in an arc from the axis of rotation of the wheel.
Thus far separate grinding machines have been required to grind accurately chipper and chisel-type saw chain because of the aforementioned differeing grinding positions required for these different types of chain. For example, applicant's prior U.S. Pat. No. Re. 28,057 discloses a grinding machine for sharpening chisel bit chain in which the machine is designed to position the chisel cutter teeth at the periphery of the grinding wheel at about 45 degrees to either side of the median plane of the wheel. On the other hand, applicant's prior U.S. Pat. No. 3,779,103 shows a grinding machine specifically designed for sharpening chipper chain by positioning the cutter teeth for sharpening at the center of the peripheral edge of the wheel. In some newer types of saw chain still having generally hook-shaped teeth, the optimum position for grinding is along the peripheral edge of the wheel somewhere between the aforementioned center grinding position and the 45-degree grinding position.
In known grinding machines for grinding chisel bit chain, two linear movements are used to bring the cutter tooth into grinding engagement with the wheel at the desired grinding position along the edge of the wheel. These two linear movements are at right angles to one another. One of such movements is generally perpendicular to the median plane of the wheel and the other movement is generally parallel to such median plane. The difficulty with this arrangement is that as the wheel wears to reduce its diameter, the angular position of grinding engagement of the cutter teeth along the edge of the wheel changes greatly to vary one or more of the cutting angles ground on the cutter teeth. As a result, different teeth of the same chain will have different cutting angles. A saw chain with cutters having different cutting angles performs poorly and dulls rapidly. If the wheel wear is appreciable without compensating adjustment, the wheel tends to grind a backslope in the vertical cutting edge of the cutter tooth. This is undesirable because a backslope causes the chain to feed poorly into the wood when cutting wood, thereby necessitating frequent regrinding and shortening the life of the chain.
A separate compensating adjustment of the grinding wheel is thus required to prevent the foregoing from happening, if such a compensating adjustment is available on the particular grinder. This compensating adjustment for wheel wear is commonly a movement of the center axis of the wheel toward the saw chain holder. However, in present grinders such an adjustment for wheel wear, being a separate adjustment, interrupts the grinding operation and therefore increases the time required to sharpen a saw chain. Moreover, such an adjustment is usually inconvenient to make, and requires skill and judgement to determine when needed. Therefore, the tendency is for grinder operators to wait too long before making such an adjustment or to ignore the need for adjustment entirely.